Overview
The progenitor of the family was Dermot mac Tadhg Mor, 7th king of Moylurg, who reigned from 1124 to 1159. He was a vassal and kinsman of the O Conchobhair Kings of Connacht; their common ancestor was Tadg mac Cathal, King of Connacht from 925 to 956.
Later off-shoot septs of the dynasty included the families of MacDermot Roe.
Moylurg ceased to exist as a kingdom in the late 16th century, though the senior line of the MacDermot's continued to live a sometime poverty-stricken and precarious existence despite land confiscations and the oppression of the Penal Laws. During this era they were popularly accorded the title Prince of Coolavin; the current incumbent is Rory MacDermot, who succeeded his father in 2003.
Read more about this topic: Mac Diarmata